Portable electronic devices are often powered by a rechargeable battery when the electronic device consumes power at a rate that makes the use of primary (non-rechargeable) battery cells cost prohibitive. Common examples of such devices are communication devices, such as cellular telephones and portable two-way radios. Operating radio and other circuitry in these types of devices requires a substantial amount of energy over time, such that primary battery cells would be depleted so often as to make use of primary battery cells impractical.
However, the use of rechargeable batteries requires a battery charger. In older systems, a battery (hereafter referring to a battery pack including one or more rechargeable battery cells) would have to be removed and connected to a charger, or the battery would be provided with external charger contacts, in addition to device contacts for powering the device, so that a charger could charge the battery while it was connected to the device. In more recent years, as technology has advanced, devices have been designed to include some, if not all of the charging function in circuitry in the device. By including charging circuitry in the device, an external power source can be connected to the device, and power from the power source can be controlled by the charging circuitry in the device to charge the battery while it is connected to the device (often even disposed inside a housing of the device).
A common means of providing power to an internal charger system is through a connector such a universal serial bus (USB) connector. There are several standards published by the USB Implementers Forum (USB-IF) that specify various electrical and mechanical parameters and features as to the form factor of the connectors as well as the electrical operation of signals over conductors contained within such connectors. Most standardized USB connections, however, are limited to a five volt power supply. For devices that are powered by, for example, a single lithium ion battery cell, which has a nominal maximum operating voltage of about 4.2 volts, a USB connection can be used to charge the single cell battery. However, in some applications, the device is designed to operate at a higher voltage, and the battery used to power the device includes series-connected battery cells producing a battery voltage that is greater than the five volts provided by a USB connection.
Accordingly, there is a need for a method and apparatus for an internal charger system for a portable electronic device that avoids the problems associated with the prior art and allows charging from an external power source through a standardized data connector when the battery voltage exceeds the voltage provided by the external power source.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.